Pope Francis in his Palm Sunday homily decried what he called indifference to the refugees flooding into Europe, making a comparison to authorities who washed their hands of Jesus' fate ahead of his crucifixion.

Before celebrating an outdoor Mass, Francis led a procession through St. Peter's Square to usher in Holy Week, the solemn period leading to Easter. Faithful Catholics clutching olive branches and braided palm fronds received his blessing.

Francis abandoned his homily text to lament Europe's handling of the influx of migrants and asylum-seekers fleeing war, persecution or poverty from Syria, Iraq, Africa and elsewhere.

Palm Sunday recalls a crowd's triumphant welcome of Jesus entering Jerusalem. But soon Jesus would be condemned to be crucified after a series of authorities declined to rule on his fate. Francis drew a parallel to that with some European countries' refusal to take responsibility for some of the more than 1 million refugees who reached European Union shores last year after risky sea voyages arranged by smugglers.

Jesus was "denied every justice," the pope said. "Jesus also suffered on his own skin indifference, because no one wanted to take on the responsibility for his destiny."

"And I am thinking of so many people, so many on the margins, so many refugees" for whom "many don't want to assume responsibility for their destiny," Francis said in a clear reference to Europe's migration debate.

In an effort to fight the smuggling, EU and Turkish officials just made a deal to send back to Turkey migrants now arriving on Greek islands. The action was to begin Sunday, but it was not clear if that would be the case.

After the Mass, Francis joyfully greeted tens of thousands of people as he toured the square in his white popemobile, and let some children aboard for a while.